1. Field of the Invention
This invention relates generally to multiple layer coatings and coating methods for hard metal or metal alloy substrates, and is particularly concerned with such coatings and methods for application to dental devices such as abutments or bars for attachment of dentures, partial dentures, crowns and the like to implants and tooth roots, or for application to surfaces of dental implants such as transgingival or bone level implants and the like.
2. Related Art
Dental devices such as implants for attachment to an existing tooth root, abutments for releasable or fixed attachment of partial or full denture devices to implants or tooth roots, single tooth abutments for attachment to crowns, transgingival implants for patients with bone loss, and implant bars are typically made from biocompatible metals such as pure titanium, titanium alloy, stainless steel or cobalt chrome. Such materials are susceptible to damage and wear, particularly in the case of abutments for removable attachment to an overdenture or the like which is repeatedly removed by the patient or the dentist for cleaning or replacement. Such dental devices are often coated with a layer of titanium nitride which is harder than the metal of the device itself, but this material is also brittle and can flake off with time. Another issue is appearance. The metal tooth abutment for attachment of a crown can appear between the gum line and crown over time, and also is darker than the crown material and can often be seen through the gum, above the gum, or through the crown. The same applies to transgingival implants which can extend one to two mm above the bone level and be visible through the gum or above the gum. Such implants are sometimes coated with a pink layer of material for aesthetic reasons, but this layer becomes damaged over time with repeated cleanings and the like.